Lauren Molina and Jason Tam are a winning couple in “Marry Me a Little,” and they look good in their undies. Photo: Carol Rosegg

Stephen Sondheim’s musicals have been called textbook examples of integration — stories told through a seamless fusion of book and songs.

And yet many of Sondheim’s tunes easily stand on their own, so much so that tributes and cobbled-up revues — “Side by Side by Sondheim,” “Putting It Together,” “Sondheim on Sondheim” — have become a thriving cottage industry.

Among the most creative of those patchworks is “Marry Me a Little,” which reopened last night in a likable revival starring Lauren Molina (“Sweeney Todd”) and Jason Tam (“Lysistrata Jones”).

Back in 1980, actor-turned-playwright Craig Lucas (“Prelude to a Kiss”) and the late director Norman René gave themselves quite a challenge: They decided to tell the story of two lonely 20-somethings exclusively through Sondheim songs. And obscure ones at that, having either been cut from major works or featured in minor ones, like the made-for-TV “Evening Primrose” (1966) and “Saturday Night,” a 1955 musical that wasn’t produced until ’97.

It worked. Even though the numbers were written decades apart for disparate shows, they feel right coming from a pair of Brooklynites looking for love. The kicker: The hotties are unaware that they live in the same building.

In Jonathan Silverstein’s staging for the Keen Company, “Him” and “Her” share the stage, which represents their respective pads. Despite crossing each other and sitting at the same table, they’re alone . . . and lonely.

“I’m on my own on a Saturday night,” they sing together yet separately, backed by John Bell on the piano. “With no one to phone on a Saturday night.”

The song list has seen some minor changes, including the addition of “Rainbows,” written for an unmade movie of “Into the Woods.”

The show has also been revised for the 21st century. The man croons “Bring on the Girls” — one of six songs plucked from “Follies” — while ogling his laptop.

The woman snaps photos of herself on her phone and checks her updates. Less cyber-savvy but just as effective is Molina’s skill on the cello — she also played it as Johanna in “Sweeney Todd” — which is smartly integrated into the plot.

Throughout the trim 70-minute production, it’s clear that these two are meant for each other. Molina overpowers Tam in the vocal department, but they both have a relaxed charm and look terrific in their underwear.